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<body class="article">
<div id="header">
<h1>tpl User Guide</h1>
<span id="author">Troy D. Hanson</span><br />
<span id="email"><tt>&lt;<a href="mailto:tdh@tkhanson.net">tdh@tkhanson.net</a>&gt;</tt></span><br />
<span id="revnumber">version 1.5,</span>
<span id="revdate">February 2010</span>
<div id="toc">
  <div id="toctitle">Table of Contents</div>
  <noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>To download tpl, follow this link back to the
<a href="https://github.com/troydhanson/tpl">GitHub project page</a>.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_overview">Overview</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_serialization_in_c">Serialization in C</h3>
<div class="paragraph"><p>Tpl is a library for serializing C data. The data is stored in its natural
binary form. The API is small and tries to stay "out of the way".
Tpl can serialize many C data types, including structures.</p></div>
</div>
<div class="sect2">
<h3 id="_uses_for_tpl">Uses for tpl</h3>
<div class="paragraph"><p>Tpl makes a convenient file format. For example, suppose a program needs to
store a list of user names and ids. This can be expressed using the format
string <tt>A(si)</tt>.  If the program needs two such lists (say, one for regular
users and one for administrators) this could be expressed as <tt>A(si)A(si)</tt>. It
is easy to read and write this kind of structured data using tpl.</p></div>
<div class="paragraph"><p>Tpl can also be used as an IPC message format. It handles byte order issues
and deframing individual messages off of a stream automatically.</p></div>
</div>
<div class="sect2">
<h3 id="_expressing_type">Expressing type</h3>
<div class="paragraph"><p>The "data type" of a tpl is explicitly stated as a format string. There is
never any ambiguity about the type of data stored in a tpl.  Some examples:</p></div>
<div class="ulist"><ul>
<li>
<p>
<tt>A(is)</tt> is a variable-length array of integer-string pairs
</p>
</li>
<li>
<p>
<tt>A(is)A(is)</tt> are two such arrays, completely independent of one another
</p>
</li>
<li>
<p>
<tt>S(ci)</tt> is a structure containing a char and integer
</p>
</li>
<li>
<p>
<tt>S(ci)#</tt> is a fixed-length array of the latter structure
</p>
</li>
<li>
<p>
<tt>A(A(i))</tt> is a nested array, that is, an array of integer arrays
</p>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_the_tpl_image">The tpl image</h3>
<div class="paragraph"><p>A tpl image is the serialized form of a tpl, stored in a memory buffer or file,
or written to a file descriptor.</p></div>
<div class="sect3">
<h4 id="_what_8217_s_in_a_tpl_image">What&#8217;s in a tpl image?</h4>
<div class="paragraph"><p>There is no need to understand the internal structure of the tpl image. But for the
curious, the image is a strictly defined binary buffer having two sections,
a header and the data.  The header encodes the length of the image, its
format string, endian order and other flags. The data section contains the
packed data.</p></div>
</div>
<div class="sect3">
<h4 id="_no_framing_needed">No framing needed</h4>
<div class="paragraph"><p>A property of the tpl image is that consecutive images can be written to a stream
without requiring any delimiter between them. The reader making use of
<tt>tpl_gather</tt> (or <tt>tpl_load</tt> in <tt>TPL_FD</tt> mode) will obtain exactly one tpl image at
a time.  Therefore tpl images can be used as an IPC message format without any
higher-level framing protocol.</p></div>
</div>
<div class="sect3">
<h4 id="_data_portability">Data portability</h4>
<div class="paragraph"><p>A tpl image generated on one kind of CPU will generally be portable to other
CPU types when tpl is used properly. This may be a surprise considering that
tpl is a binary format. But tpl has been carefully designed to make this work.
Each <a href="#types">format character</a> has an associated explicitly-sized type. For
integer and floating point types, whose "endian" or byte-order convention varies
from one CPU to another, tpl automatically and transparently corrects the
endian order (if needed) during the unpacking process.  Floating point numbers
present their own <a href="#trouble_with_double">special difficulties</a>. <em>No guarantees
are made with regard to floating point portability.</em> That said, because many
modern CPU&#8217;s use IEEE 754 floating point representation, data is likely to be
portable among them.</p></div>
</div>
</div>
<div class="sect2">
<h3 id="_xml_and_perl">XML and Perl</h3>
<div class="paragraph"><p><em>Note: The <tt>tplxml</tt> utility and the Perl module are currently unsupported in tpl 1.5.</em></p></div>
<div class="sect3">
<h4 id="_xml">XML</h4>
<div class="paragraph"><p>While a tpl image is a binary entity, you can view any tpl image in XML format
using the included <tt>tplxml</tt> utility, located in the <tt>lang/perl</tt> directory.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tplxml file.tpl &gt; file.xml
tplxml file.xml &gt; file.tpl</tt></pre>
</div></div>
<div class="paragraph"><p>The utility is bidirectional, as shown.  The file extension is not important;
<tt>tplxml</tt> inspects its input to see if it&#8217;s tpl or XML. You can also pipe data
into it instead of giving it a filename. The <tt>tplxml</tt> utility is slow. Its
purpose is two-fold: debugging (manual inspection of the data in a tpl), and
interoperability with XML-based programs.  The resulting XML is often ten times
the size of the original binary tpl image.</p></div>
</div>
<div class="sect3">
<h4 id="_perl">Perl</h4>
<div class="paragraph"><p>There is a Perl module in <tt>lang/perl/Tpl.pm</tt>. The <a href="perl.html">Perl API</a>
is convenient for writing Perl scripts that interoperate with C programs, and
need to pass structured data back and forth. It is written in pure Perl.</p></div>
</div>
</div>
<div class="sect2">
<h3 id="_platforms">Platforms</h3>
<div class="paragraph"><p>The tpl software was developed for POSIX systems and has been tested on 32- and 64-bit
platforms including:</p></div>
<div class="ulist"><ul>
<li>
<p>
Linux
</p>
</li>
<li>
<p>
Solaris
</p>
</li>
<li>
<p>
Mac OS X
</p>
</li>
<li>
<p>
OpenBSD
</p>
</li>
<li>
<p>
Windows using Visual Studio 2008 or 2010, or Cygwin or MinGW
</p>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_bsd_licensed">BSD licensed</h3>
<div class="paragraph"><p>This software is made available under the
<a href="license.html">revised BSD license</a>.
It is free and open source.</p></div>
</div>
<div class="sect2">
<h3 id="_download">Download</h3>
<div class="paragraph"><p>You can clone tpl, or get a zipfile, from the
<a href="https://github.com/troydhanson/tpl">GitHub project page</a>.</p></div>
</div>
<div class="sect2">
<h3 id="_contributing">Contributing</h3>
<div class="paragraph"><p>If you add a new feature or fix something in tpl or in the extras, please
make a pull request on Github. For anything other than a trivial change, include
a unit test and documentation if you possibly can. (And don&#8217;t be discouraged if
it takes weeks or even months for me to merge it. Sorry, my life is busy!) Thanks!</p></div>
</div>
<div class="sect2">
<h3 id="_news">News</h3>
<div class="paragraph"><p>The author has a blog for <a href="http://troydhanson.wordpress.com/">software updates</a>
<span class="image">
<img src="rss.png" alt="(RSS)" />
</span>. You can also follow @troydhanson on Twitter for updates.</p></div>
<div class="sect3">
<h4 id="_other_software">Other software</h4>
<div class="paragraph"><p>Other open-source software by the author is listed at
<a href="http://troydhanson.github.io">http://troydhanson.github.io</a></p></div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_build_and_install">Build and install</h2>
<div class="sectionbody">
<div class="paragraph"><p>Tpl has no dependencies on libraries other than the system C library. You
can simply copy the tpl source into your project, so you have no dependencies.
Alternatively, you can build tpl as a library and link it to your program.</p></div>
<div class="sect2">
<h3 id="_as_source">As source</h3>
<div class="paragraph"><p>The simplest way to use tpl is to copy the source files <tt>tpl.h</tt> and <tt>tpl.c</tt>
(from the <tt>src/</tt> directory) right into your project, and build them with the
rest of your source files. No special compiler flags are required.</p></div>
</div>
<div class="sect2">
<h3 id="_as_a_library">As a library</h3>
<div class="paragraph"><p>Alternatively, to build tpl as a library, from the top-level directory, run:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>./configure
make
make install</tt></pre>
</div></div>
<div class="paragraph"><p>(Note that, if <tt>configure</tt> is missing, generate it by running <tt>bootstrap</tt>.)</p></div>
<div class="paragraph"><p>This installs a static library <tt>libtpl.a</tt> and a shared library (e.g.,
<tt>libtpl.so</tt>), if your system supports them, in standard places. The installation
directory can be customized using <tt>./configure --prefix=/some/directory</tt>. Run
<tt>configure --help</tt> for further options.</p></div>
<div class="sect3">
<h4 id="_test_suite">Test suite</h4>
<div class="paragraph"><p>You can compile and run the built-in test suite by running:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>cd tests/
make</tt></pre>
</div></div>
</div>
</div>
<div class="sect2">
<h3 id="_on_windows">On Windows</h3>
<div class="sect3">
<h4 id="_compile_in">Compile-in</h4>
<div class="paragraph"><p>Tpl can be used directly (instead of as a DLL) by compiling the tpl sources
right into your program. To do this, add <tt>tpl.c</tt>, <tt>tpl.h</tt>, <tt>win/mman.h</tt> and
<tt>win/mmap.c</tt> to your program&#8217;s source and header files and add the preprocessor
definition <tt>TPL_NOLIB</tt>.</p></div>
</div>
<div class="sect3">
<h4 id="_dll">DLL</h4>
<div class="paragraph"><p>If you like, you can build the DLL yourself using VS2008 or VS2010 (the
free Express Edition is sufficient) and perhaps newer versions, though this has
not been tested by the author. (As of 2013 we need to restore the solution file
to make this easy, that&#8217;s currently missing).</p></div>
</div>
<div class="sect3">
<h4 id="_mingw_cygwin">MinGW/Cygwin</h4>
<div class="paragraph"><p>You can build it in the traditional Unix method under Cygwin/MinGW using the
"configure; make; make install" approach. If the "configure" script is not
present in the repository you cloned, generate it by running "bootstrap".</p></div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_api_concepts">API concepts</h2>
<div class="sectionbody">
<div class="paragraph"><p>To use tpl, you need to know the order in which to call the API functions, and
the background concepts of format string, arrays and index numbers.</p></div>
<div class="sect2">
<h3 id="_order_of_functions">Order of functions</h3>
<div class="paragraph"><p>Creating a tpl is always the first step, and freeing it is the last step. In
between, you either pack and dump the tpl (if you&#8217;re serializing data) or you
load a tpl image and unpack it (if you&#8217;re deserializing data).</p></div>
<div class="tableblock">
<table rules="none"
width="50%"
frame="border"
cellspacing="0" cellpadding="4">
<caption class="title">Table 1. Order of usage</caption>
<col width="9%" />
<col width="45%" />
<col width="45%" />
<thead>
<tr>
<th align="center" valign="top">Step  </th>
<th align="center" valign="top">     If you&#8217;re serializing&#8230;</th>
<th align="center" valign="top">      If you&#8217;re deserializing&#8230;</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center" valign="top"><p class="table">1.</p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_map()</tt></p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_map()</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">2.</p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_pack()</tt></p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_load()</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">3.</p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_dump()</tt></p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_unpack()</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">4.</p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_free()</tt></p></td>
<td align="center" valign="top"><p class="table"><tt>tpl_free()</tt></p></td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="sect2">
<h3 id="format">Format string</h3>
<div class="paragraph"><p>When a tpl is created using <tt>tpl_map()</tt>, its data type is expressed as a format
string.  Each character in the format string has an associated argument of a
specific type.  For example, this is how a format string and its arguments are
passed in to <tt>tpl_map</tt>:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tpl_node *tn;
char c;
int i[10];
tn = tpl_map("ci#", &amp;c, i, 10);  /* ci# is our format string */</tt></pre>
</div></div>
<div class="tableblock" id="types">
<table rules="none"
width="90%"
frame="border"
cellspacing="0" cellpadding="4">
<caption class="title">Table 2. Supported format characters</caption>
<col width="11%" />
<col width="44%" />
<col width="44%" />
<thead>
<tr>
<th align="center" valign="top">Type </th>
<th align="left" valign="top">  Description                                             </th>
<th align="left" valign="top"> Required argument type</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center" valign="top"><p class="table"><tt>j</tt></p></td>
<td align="left" valign="top"><p class="table">16-bit signed int</p></td>
<td align="left" valign="top"><p class="table">int16_t* or equivalent</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>v</tt></p></td>
<td align="left" valign="top"><p class="table">16-bit unsigned int</p></td>
<td align="left" valign="top"><p class="table">uint16_t* or equivalent</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>i</tt></p></td>
<td align="left" valign="top"><p class="table">32-bit signed int</p></td>
<td align="left" valign="top"><p class="table">int32_t* or equivalent</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>u</tt></p></td>
<td align="left" valign="top"><p class="table">32-bit unsigned int</p></td>
<td align="left" valign="top"><p class="table">uint32_t* or equivalent</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>I</tt></p></td>
<td align="left" valign="top"><p class="table">64-bit signed int</p></td>
<td align="left" valign="top"><p class="table">int64_t* or equivalent</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>U</tt></p></td>
<td align="left" valign="top"><p class="table">64-bit unsigned int</p></td>
<td align="left" valign="top"><p class="table">uint64_t* or equivalent</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>c</tt></p></td>
<td align="left" valign="top"><p class="table">character (byte)</p></td>
<td align="left" valign="top"><p class="table">char*</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>s</tt></p></td>
<td align="left" valign="top"><p class="table">string</p></td>
<td align="left" valign="top"><p class="table">char**</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>f</tt></p></td>
<td align="left" valign="top"><p class="table">64-bit double precision float</p></td>
<td align="left" valign="top"><p class="table">double* (varies by platform)</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>#</tt></p></td>
<td align="left" valign="top"><p class="table">array length; modifies preceding <tt>iujvIUcsf</tt> or <tt>S(...)</tt></p></td>
<td align="left" valign="top"><p class="table">int</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>B</tt></p></td>
<td align="left" valign="top"><p class="table">binary buffer (arbitrary-length)</p></td>
<td align="left" valign="top"><p class="table">tpl_bin*</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>S</tt></p></td>
<td align="left" valign="top"><p class="table">structure (&#8230;)</p></td>
<td align="left" valign="top"><p class="table">struct *</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>$</tt></p></td>
<td align="left" valign="top"><p class="table">nested structure (&#8230;)</p></td>
<td align="left" valign="top"><p class="table">none</p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table"><tt>A</tt></p></td>
<td align="left" valign="top"><p class="table">array (&#8230;)</p></td>
<td align="left" valign="top"><p class="table">none</p></td>
</tr>
</tbody>
</table>
</div>
<div class="sect3">
<h4 id="_explicit_sizes">Explicit sizes</h4>
<div class="paragraph"><p>The sizes of data types such as <tt>long</tt> and <tt>double</tt> vary by platform. This must
be kept in mind because most tpl format characters require a pointer argument to
a specific-sized type, listed above. You can use explicit-sized types such as
<tt>int32_t</tt> (defined in <tt>inttypes.h</tt>) in your program if you find this helpful.</p></div>
<div class="sect4">
<h5 id="trouble_with_double">The trouble with double</h5>
<div class="paragraph"><p>Unfortunately there are no standard explicit-sized floating-point types-- no
<tt>float64_t</tt>, for example. If you plan to serialize <tt>double</tt> on your platform
using tpl&#8217;s <tt>f</tt> format character, first be sure that your <tt>double</tt> is 64 bits.
Second, if you plan to deserialize it on a different kind of CPU, be sure that
both CPU&#8217;s use the same floating-point representation such as IEEE 754.</p></div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="arrays">Arrays</h3>
<div class="paragraph"><p>Arrays come in two kinds: <strong>fixed-length</strong> and <strong>variable-length</strong> arrays.
Intuitively, they can be thought of like conventional C arrays and linked lists.
In general, use fixed-length arrays if possible, and variable-length arrays
if necessary. The variable-length arrays support more complex data types, and
give or receive the elements to your program one by one.</p></div>
<div class="sect3">
<h4 id="_fixed_length_vs_variable_length_arrays">Fixed-length vs. Variable-length arrays</h4>
<div class="dlist"><dl>
<dt class="hdlist1">
Notation
</dt>
<dd>
<p>
    Fixed-length arrays are denoted like <tt>i#</tt> (a simple type followed by one or
    more <tt>#</tt> signs), but variable-length arrays are denoted like <tt>A(i)</tt>.
</p>
</dd>
<dt class="hdlist1">
Element handling
</dt>
<dd>
<p>
    All the elements of a fixed-length array are packed or unpacked at once. But
    the elements of a variable-length array are packed or unpacked one by one.
</p>
</dd>
<dt class="hdlist1">
Array length
</dt>
<dd>
<p>
    The number of elements in a fixed-length array is specified before use--
    before any data is packed. But variable-length arrays do not have a fixed
    element count. They can have any number of elements packed into them. When
    unpacking a variable-length array, they are unpacked one by one until they
    are exhausted.
</p>
</dd>
<dt class="hdlist1">
Element types
</dt>
<dd>
<p>
    Elements of fixed-length arrays can be the integer, byte, double, string
    types or structures. (This excludes format characters <tt>BA</tt>).  Fixed-length
    arrays can also be multi-dimensional like <tt>i##</tt>. Variable-length arrays can
    have simple or complex elements-- for example, an array of ints <tt>A(i)</tt>, an
    array of int/double pairs <tt>A(if)</tt>, or even nested arrays like <tt>A(A(if))</tt>.
</p>
</dd>
</dl></div>
<div class="paragraph"><p>Before explaining all the concepts, it&#8217;s illustrative to see how both kinds of
arrays are used. Let&#8217;s pack the integers 0 through 9 both ways.</p></div>
<div class="listingblock" id="fixed_pack">
<div class="title">Packing 0-9 as a fixed-length array</div>
<div class="content">
<pre><tt>#include "tpl.h"
int main() {
    tpl_node *tn;
    int x[] = {0,1,2,3,4,5,6,7,8,9};

    tn = tpl_map("i#", x, 10);
    tpl_pack(tn,0);                         /* pack all 10 elements at once */
    tpl_dump(tn, TPL_FILE, "/tmp/fixed.tpl");
    tpl_free(tn);
}</tt></pre>
</div></div>
<div class="paragraph"><p>Note that the length of the fixed-length array (10) was passed as an argument to
<tt>tpl_map()</tt>.  The corresponding unpacking <a href="#fixed_unpack">example</a> is listed
further below. Now let&#8217;s see how we would pack 0-9 as a variable-length array:</p></div>
<div class="listingblock">
<div class="title">Packing 0-9 as a variable-length array</div>
<div class="content">
<pre><tt>#include "tpl.h"
int main() {
    tpl_node *tn;
    int x;

    tn = tpl_map("A(i)", &amp;x);
    for(x = 0; x &lt; 10; x++) tpl_pack(tn,1);  /* pack one element at a time */
    tpl_dump(tn, TPL_FILE, "/tmp/variable.tpl");
    tpl_free(tn);
}</tt></pre>
</div></div>
<div class="paragraph"><p>Notice how we called <tt>tpl_pack</tt> in a loop, once for each element 0-9. Again,
there is a corresponding unpacking <a href="#var_unpack">example</a> shown later in the
guide. You might also notice that this time, we passed 1 as the final argument
to tpl_pack. This is an index number designating which variable-length array
we&#8217;re packing. In this case, there is only one.</p></div>
</div>
<div class="sect3">
<h4 id="index">Index numbers</h4>
<div class="paragraph"><p>Index numbers identify a particular variable-length array in the format string.
Each <tt>A(...)</tt> in a format string has its own index number.  The index numbers
are assigned left-to-right starting from 1. Examples:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>A(i)        /* index number 1 */
A(i)A(i)    /* index numbers 1 and 2 */
A(A(i))     /* index numbers 1 and 2 (order is independent of nesting) */</tt></pre>
</div></div>
<div class="sect4">
<h5 id="_special_index_number_0">Special index number 0</h5>
<div class="paragraph"><p>The special index number 0 designates all the format characters that are not
inside an <tt>A(...)</tt>.  Examples of what index 0 does (and does not) designate:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>S(ius)      /* index 0 designates the whole thing */
iA(c)u      /* index 0 designates the i and the u */
c#A(i)S(ci) /* index 0 designates the c# and the S(ci) */</tt></pre>
</div></div>
<div class="paragraph"><p>An index number is passed to <tt>tpl_pack</tt> and <tt>tpl_unpack</tt> to specify which
variable-length array (or non-array, in the case of index number 0) to act upon.</p></div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_integers">Integers</h3>
<div class="paragraph"><p>The array examples <a href="#fixed_pack">above</a> demonstrated how integers could be
packed.  We&#8217;ll show some further examples here of unpacking integers and dealing
with multi-dimensional arrays. The same program could be used to demonstrate
working with byte, 16-bit shorts, 32-bit or 64-bit signed and unsigned integers
with only a change to the data type and the format character.</p></div>
<div class="listingblock" id="fixed_unpack">
<div class="title">Unpacking 0-9 from a fixed-length array</div>
<div class="content">
<pre><tt>#include "tpl.h"
int main() {
    tpl_node *tn;
    int x[10];

    tn = tpl_map("i#", x, 10);
    tpl_load(tn, TPL_FILE, "/tmp/fixed.tpl");
    tpl_unpack(tn,0);  /* unpack all 10 elements at once */
    tpl_free(tn);
    /* now do something with x[0]...x[9].. (not shown) */
}</tt></pre>
</div></div>
<div class="paragraph"><p>For completeness, let&#8217;s also see how to unpack a variable-length integer array.</p></div>
<div class="listingblock" id="var_unpack">
<div class="title">Unpacking 0-9 from a variable-length array</div>
<div class="content">
<pre><tt>#include "tpl.h"
int main() {
    tpl_node *tn;
    int x;

    tn = tpl_map("A(i)", &amp;x);
    tpl_load(tn, TPL_FILE, "/tmp/variable.tpl");
    while (tpl_unpack(tn,1) &gt; 0) printf("%d\n",x); /* unpack one by one */
    tpl_free(tn);
}</tt></pre>
</div></div>
<div class="sect3">
<h4 id="multidim_int">Multi-dimensional arrays</h4>
<div class="paragraph"><p>A multi-dimensional matrix of integers can be packed and unpacked the same way
as any fixed-length array.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>int xy[XDIM][YDIM];
...
tn = tpl_map("i##", xy, XDIM, YDIM);
tpl_pack(tn, 0);</tt></pre>
</div></div>
<div class="paragraph"><p>This single call to <tt>tpl_pack</tt> packs the entire matrix.</p></div>
</div>
</div>
<div class="sect2">
<h3 id="_strings">Strings</h3>
<div class="paragraph"><p>Tpl can serialize C strings. A different format is used for <tt>char*</tt> vs. <tt>char[ ]</tt>
as described below. Let&#8217;s look at <tt>char*</tt> first:</p></div>
<div class="listingblock">
<div class="title">Packing a string</div>
<div class="content">
<pre><tt>    #include "tpl.h"

    int main() {
        tpl_node *tn;
        char *s = "hello, world!";
        tn = tpl_map("s", &amp;s);
        tpl_pack(tn,0);  /* copies "hello, world!" into the tpl */
        tpl_dump(tn,TPL_FILE,"string.tpl");
        tpl_free(tn);
    }</tt></pre>
</div></div>
<div class="paragraph"><p>The <tt>char*</tt> must point to a null-terminated string or be a <tt>NULL</tt> pointer.</p></div>
<div class="paragraph"><p>When deserializing (unpacking) a C string, space for it will be allocated
automatically, but you are responsible for freeing it (unless it is <tt>NULL</tt>):</p></div>
<div class="listingblock">
<div class="title">Unpacking a string</div>
<div class="content">
<pre><tt>    #include "tpl.h"

    int main() {
        tpl_node *tn;
        char *s;
        tn = tpl_map("s", &amp;s);
        tpl_load(tn,TPL_FILE,"string.tpl");
        tpl_unpack(tn,0);   /* allocates space, points s to "hello, world!" */
        printf("unpacked %s\n", s);
        free(s);            /* our responsibility to free s */
        tpl_free(tn);
    }</tt></pre>
</div></div>
<div class="sect3">
<h4 id="_char_vs_char">char* vs char[ ]</h4>
<div class="paragraph"><p>The <tt>s</tt> format character is only for use with <tt>char*</tt> types. In the example
above, <tt>s</tt> is a <tt>char*</tt>. If it had been a <tt>char s[14]</tt>, we would use the format
characters <tt>c#</tt> to pack or unpack it, as a fixed-length character array. (This
unpacks the characters "in-place", instead of into a dynamically allocated
buffer). Also, a fixed-length buffer described by <tt>c#</tt> need not be
null-terminated.</p></div>
</div>
<div class="sect3">
<h4 id="_arrays_of_strings">Arrays of strings</h4>
<div class="paragraph"><p>You can use fixed- or variable-length arrays of strings in tpl. An example of
packing a fixed-length two-dimensional array of strings is shown here.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>char *labels[2][3] = { {"one", "two", "three"},
                       {"eins", "zwei", "drei" } };
tpl_node *tn;
tn = tpl_map("s##", labels, 2, 3);
tpl_pack(tn,0);
tpl_dump(tn,TPL_FILE,filename);
tpl_free(tn);</tt></pre>
</div></div>
<div class="paragraph"><p>Later, when unpacking these strings, the programmer must remember to free them
one by one, after they are no longer needed.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>char *olabels[2][3];
int i,j;</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map("s##", olabels, 2, 3);
tpl_load(tn,TPL_FILE,filename);
tpl_unpack(tn,0);
tpl_free(tn);</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>for(i=0;i&lt;2;i++) {
  for(j=0;j&lt;3;j++) {
    printf("%s\n", olabels[i][j]);
    free(olabels[i][j]);
  }
}</tt></pre>
</div></div>
</div>
</div>
<div class="sect2">
<h3 id="_binary_buffers">Binary buffers</h3>
<div class="paragraph"><p>Packing an arbitrary-length binary buffer (tpl format character <tt>B</tt>) makes use
of the <tt>tpl_bin</tt> structure.  You must declare this structure and populate it
with the address and length of the binary buffer to be packed.</p></div>
<div class="listingblock">
<div class="title">Packing a binary buffer</div>
<div class="content">
<pre><tt>    #include "tpl.h"
    #include &lt;sys/time.h&gt;

    int main() {
        tpl_node *tn;
        tpl_bin tb;

        /* we'll use a timeval as our guinea pig */
        struct timeval tv;
        gettimeofday(&amp;tv,NULL);

        tn = tpl_map( "B", &amp;tb );
        tb.sz = sizeof(struct timeval);  /* size of buffer to pack */
        tb.addr = &amp;tv;                   /* address of buffer to pack */
        tpl_pack( tn, 0 );
        tpl_dump(tn, TPL_FILE, "bin.tpl");
        tpl_free(tn);
    }</tt></pre>
</div></div>
<div class="paragraph"><p>When you unpack a binary buffer, tpl will automatically allocate it, and will
populate your <tt>tpl_bin</tt> structure with its address and length. You are
responsible for eventually freeing the buffer.</p></div>
<div class="listingblock">
<div class="title">Unpacking a binary buffer</div>
<div class="content">
<pre><tt>    #include "tpl.h"

    int main() {
        tpl_node *tn;
        tpl_bin tb;

        tn = tpl_map( "B", &amp;tb );
        tpl_load( tn, TPL_FILE, "bin.tpl" );
        tpl_unpack( tn, 0 );
        tpl_free(tn);

        printf("binary buffer of length %d at address %p\n", tb.sz, tb.addr);
        free(tb.addr);  /* our responsibility to free it */
    }</tt></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_structures">Structures</h3>
<div class="paragraph"><p>You can use tpl to pack and unpack structures, and arrays of structures.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>struct ci {
    char c;
    int i;
};
struct ci s = {'a', 1};</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map("S(ci)", &amp;s);  /* pass structure address */
tpl_pack(tn, 0);
tpl_dump(tn, TPL_FILE, "struct.tpl");
tpl_free(tn);</tt></pre>
</div></div>
<div class="paragraph"><p>As shown, omit the individual arguments for the format characters inside the
parenthesis. The exception is for fixed-length arrays; when <tt>S(...)</tt> contains a
<tt>#</tt> character, its length argument is required: <tt>tpl_map("S(f#i)", &amp;s, 10);</tt></p></div>
<div class="paragraph"><p>When using the <tt>S(...)</tt> format, the only characters allowed inside the
parentheses are <tt>iujvcsfIU#$()</tt>.</p></div>
<div class="sect3">
<h4 id="_structure_arrays">Structure arrays</h4>
<div class="paragraph"><p>Arrays of structures are the same as simple arrays. Fixed- or variable- length
arrays are supported.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>struct ci sa[100], one;</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map("S(ci)#", sa, 100);  /* fixed-length array of 100 structures */
tn = tpl_map("A(S(ci))", &amp;one);   /* variable-length array (one at a time) */</tt></pre>
</div></div>
<div class="paragraph"><p>The differences between fixed- and variable-length arrays are explained in the
<a href="#arrays">Arrays</a> section.</p></div>
</div>
<div class="sect3">
<h4 id="_nested_structures">Nested structures</h4>
<div class="paragraph"><p>When dealing with nested structures, the outermost structure uses the <tt>S</tt> format
character, and the inner nested structures use the <tt>$</tt> format. Only the
<em>outermost</em> structure&#8217;s address is given to <tt>tpl_map</tt>.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>struct inner_t {
  char a;
}</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>struct outer_t {
  char b;
  struct inner_t i;
}</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>tpl_node *tn;
struct outer_t outer = {'b', {'a'}};</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map("S(c$(c))", &amp;outer);</tt></pre>
</div></div>
<div class="paragraph"><p>Structures can nest to any level. Currently tpl does not support fixed-length
array suffixes on inner structures.  However the outermost structure can have a
length suffix even if it contains some nested structures.</p></div>
</div>
</div>
<div class="sect2">
<h3 id="_linked_lists">Linked lists</h3>
<div class="paragraph"><p>While tpl has no specific data type for a linked list, the technique for
packing them is illustrated here.  First describe your list element as a
format string and then surround it with <tt>A(...)</tt> to describe it as
variable-length array.  Then, using a temporary variable, iterate over each
list element, copying it to the temporary variable and packing it.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>struct element {
  char c;
  int i;
  struct element *next;
}</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>struct element *list, *i, tmp;
tpl_node *tn;</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>/* add some elements to list.. (not shown) */</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map("A(S(ci))", &amp;tmp);
for(i = list; i != NULL; i=i-&gt;next) {
  tmp = *i;
  tpl_pack(tn, 1);
}
tpl_dump(tn,TPL_FILE,"list.tpl");
tpl_free(tn);</tt></pre>
</div></div>
<div class="paragraph"><p>Unpacking is similar. The <tt>for</tt> loop is just replaced with:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>while( tpl_unpack(tn,1) &gt; 0) {
  struct element *newelt = malloc(sizeof(struct element));
  *newelt = tmp;
  add_to_list(list, newelt);
}</tt></pre>
</div></div>
<div class="paragraph"><p>As you can see, tpl does not reinstate the whole list at once-- just one
element at a time. You need to link the elements manually. A future release of
tpl may support <em>pointer swizzling</em> to make this easier.</p></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_api">API</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="tpl_map">tpl_map</h3>
<div class="paragraph"><p>The only way to create a tpl is to call <tt>tpl_map()</tt>. The first argument is the
<a href="#format">format string</a>. This is followed by a list of arguments as required by
the particular characters in the format string. E.g,</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tpl_node *tn;
int i;
tn = tpl_map( "A(i)", &amp;i );</tt></pre>
</div></div>
<div class="paragraph"><p>The function creates a mapping between the items in the format string and the C
program variables whose addresses are given. Later, the C variables will be read
or written as the tpl is packed or unpacked.</p></div>
<div class="paragraph"><p>This function returns a <tt>tpl_node*</tt> on success, or <tt>NULL</tt> on failure.</p></div>
</div>
<div class="sect2">
<h3 id="tpl_pack">tpl_pack</h3>
<div class="paragraph"><p>The function <tt>tpl_pack()</tt> packs data into a tpl. The arguments to
<tt>tpl_pack()</tt> are a <tt>tpl_node*</tt> and an <a href="#index">index number</a>.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map("A(i)A(c)", &amp;i, &amp;c);
for(i=0; i&lt;10; i++) tpl_pack(tn, 1);    /* pack 0-9 into index 1 */
for(c='a'; c&lt;='z'; c++) tpl_pack(tn, 2); /* pack a-z into index 2 */</tt></pre>
</div></div>
<div class="sidebarblock">
<div class="content">
<div class="title">Data is copied when packed</div>
<div class="paragraph"><p>Every call to <tt>tpl_pack()</tt> immediately <em>copies</em> the data being packed. Thus
the program is free to immediately overwrite or re-use the packed variables.</p></div>
</div></div>
<div class="sect3">
<h4 id="_index_number_0">Index number 0</h4>
<div class="paragraph"><p>It is necessary to pack index number 0 only if the format string contains
characters that are not inside an <tt>A(...)</tt>, such as the <tt>i</tt> in the format string
<tt>iA(c)</tt>.</p></div>
</div>
<div class="sect3">
<h4 id="_variable_length_arrays">Variable-length arrays</h4>
<div class="sect4">
<h5 id="_adding_elements_to_an_array">Adding elements to an array</h5>
<div class="paragraph"><p>To add elements to a variable-length array, call <tt>tpl_pack()</tt> repeatedly.  Each
call adds another element to the array.</p></div>
</div>
<div class="sect4">
<h5 id="_zero_length_arrays_are_ok">Zero-length arrays are ok</h5>
<div class="paragraph"><p>It&#8217;s perfectly acceptable to pack nothing into a variable-length array,
resulting in a zero-length array.</p></div>
</div>
<div class="sect4">
<h5 id="nested_pack">Packing nested arrays</h5>
<div class="paragraph"><p>In a format string containing a nested, variable-length array, such as
<tt>A(A(s))</tt>, the inner, child array should be packed prior to the parent array.</p></div>
<div class="paragraph"><p>When you pack a parent array, a "snapshot" of the current child array is placed
into the parent&#8217;s new element.  Packing a parent array also empties the child
array. This way, you can pack new data into the child, then pack the parent
again. This creates distinct parent elements which each contain distinct child
arrays.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">When dealing with nested arrays like <tt>A(A(i))</tt>, <em>pack</em> them from the "inside
out" (child first), but <em>unpack</em> them from the "outside in" (parent first).</td>
</tr></table>
</div>
<div class="paragraph"><p>The example below creates a tpl having the format string <tt>A(A(c))</tt>.</p></div>
<div class="listingblock">
<div class="title">Packing nested arrays</div>
<div class="content">
<pre><tt>#include "tpl.h"

int main() {
    char c;
    tpl_node *tn;

    tn = tpl_map("A(A(c))", &amp;c);

    for(c='a'; c&lt;'c'; c++) tpl_pack(tn,2);  /* pack child (twice) */
    tpl_pack(tn, 1);                        /* pack parent */

    for(c='1'; c&lt;'4'; c++) tpl_pack(tn,2);  /* pack child (three times) */
    tpl_pack(tn, 1);                        /* pack parent */

    tpl_dump(tn, TPL_FILE, "test40.tpl");
    tpl_free(tn);
}</tt></pre>
</div></div>
<div class="paragraph"><p>This creates a nested array in which the parent has two elements: the first
element is the two-element nested array <em>a</em>, <em>b</em>; and the second element is
the three-element nested array <em>1</em>, <em>2</em>, <em>3</em>.
The <a href="#nested_unpack">nested unpacking example</a> shows how this tpl is unpacked.</p></div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="tpl_dump">tpl_dump</h3>
<div class="paragraph"><p>After packing a tpl, <tt>tpl_dump()</tt> is used to write the tpl image to a file,
memory buffer or file descriptor. The corresponding modes are shown below. A
final mode is for querying the output size without actually performing the dump.</p></div>
<div class="tableblock">
<table rules="none"
width="80%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="30%" />
<col width="70%" />
<thead>
<tr>
<th align="center" valign="top">Write to&#8230;      </th>
<th align="left" valign="top">Usage</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center" valign="top"><p class="table">file</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_dump(tn, TPL_FILE, "file.tpl" );</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">file descriptor</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_dump(tn, TPL_FD, 2);</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">memory</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_dump(tn, TPL_MEM, &amp;addr, &amp;len );</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">caller&#8217;s memory</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_dump(tn, TPL_MEM|TPL_PREALLOCD, buf, sizeof(buf));</tt></p></td>
</tr>
<tr>
<td align="center" valign="top"><p class="table">just get size</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_dump(tn, TPL_GETSIZE, &amp;sz);</tt></p></td>
</tr>
</tbody>
</table>
</div>
<div class="paragraph"><p>The first argument is the <tt>tpl_node*</tt> and the second is one of these constants:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<tt>TPL_FILE</tt>
</dt>
<dd>
<p>
    Writes the tpl to a file whose name is given in the following argument.
    The file is created with permissions 664 (<tt>rw-rw-r--</tt>) unless further
    restricted by the process <tt>umask</tt>.
</p>
</dd>
<dt class="hdlist1">
<tt>TPL_FD</tt>
</dt>
<dd>
<p>
    Writes the tpl to the file descriptor given in the following argument.
    The descriptor can be either blocking or non-blocking, but will busy-loop
    if non-blocking and the contents cannot be written immediately.
</p>
</dd>
<dt class="hdlist1">
<tt>TPL_MEM</tt>
</dt>
<dd>
<p>
    Writes the tpl to a memory buffer. The following two arguments must be a
    <tt>void**</tt> and a <tt>size_t*</tt>. The function will allocate a buffer and store
    its address and length into these locations.  The caller is responsible to
    <tt>free()</tt> the buffer when done using it.
</p>
</dd>
<dt class="hdlist1">
<tt>TPL_MEM|TPL_PREALLOCD</tt>
</dt>
<dd>
<p>
    Writes the tpl to a memory buffer that the caller has already allocated or
    declared. The following two arguments must be a <tt>void*</tt> and a <tt>size_t</tt>
    specifying the buffer address and size respectively. (If the buffer is of
    insufficient size to receive the tpl dump, the function will return -1).
    This mode can be useful in conjunction with <tt>tpl_load</tt> in <tt>TPL_EXCESS_OK</tt>
    mode, as shown <a href="#excess_ok">here.</a>
</p>
</dd>
<dt class="hdlist1">
<tt>TPL_GETSIZE</tt>
</dt>
<dd>
<p>
    This special mode does not actually dump the tpl. Instead it places the size
    that the dump <em>would</em> require into the <tt>size_t</tt> pointed to by the
    following argument.
</p>
</dd>
</dl></div>
<div class="paragraph"><p>The return value is 0 on success, or -1 on error.</p></div>
<div class="paragraph"><p>The <tt>tpl_dump()</tt> function does not free the tpl.  Use <tt>tpl_free()</tt> to release
the tpl&#8217;s resources when done.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="title">Back-to-back tpl images require no delimiter</div>If you want to store a series of tpl images, or transmit sequential tpl images
over a socket (perhaps as messages to another program), you can simply dump them
sequentially without needing to add any delimiter for the individual tpl images.
Tpl images are internally delimited, so <tt>tpl_load</tt> will read just one at a time
even if multiple images are contiguous.</td>
</tr></table>
</div>
</div>
<div class="sect2">
<h3 id="tpl_load">tpl_load</h3>
<div class="paragraph"><p>This API function reads a previously-dumped tpl image from a file, memory
buffer or file descriptor, and prepares it for subsequent unpacking.  The format
string specified in the preceding call to <tt>tpl_map()</tt> will be cross-checked
for equality with the format string stored in the tpl image.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map( "A(i)", &amp;i );
tpl_load( tn, TPL_FILE, "demo.tpl" );</tt></pre>
</div></div>
<div class="paragraph"><p>The first argument to <tt>tpl_load()</tt> is the <tt>tpl_node*</tt>.  The second argument is
one of the constants:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<tt>TPL_FILE</tt>
</dt>
<dd>
<p>
    Loads the tpl from the file named in the following argument. It is also
    possible to bitwise-OR this flag with <tt>TPL_EXCESS_OK</tt> as explained below.
</p>
</dd>
<dt class="hdlist1">
<tt>TPL_MEM</tt>
</dt>
<dd>
<p>
    Loads the tpl from a memory buffer. The following two arguments must be a
    <tt>void*</tt> and a <tt>size_t</tt>, specifying the buffer address and size,
    respectively.  The caller must not free the memory buffer until after
    freeing the tpl with <tt>tpl_free()</tt>. (If the caller wishes to hand over
    responsibility for freeing the memory buffer, so that it&#8217;s automatically
    freed along with the tpl when <tt>tpl_free()</tt> is called, the constant
    <tt>TPL_UFREE</tt> may be bitwise-OR&#8217;d with <tt>TPL_MEM</tt> to achieve this).
    Furthermore, <tt>TPL_MEM</tt> may be bitwise-OR&#8217;d with <tt>TPL_EXCESS_OK</tt>, explained
    below.
</p>
</dd>
<dt class="hdlist1">
<tt>TPL_FD</tt>
</dt>
<dd>
<p>
    Loads the tpl from the file descriptor given in the following argument.
    The descriptor is read until one complete tpl image is loaded; no bytes
    past the end of the tpl image will be read.  The descriptor can be either
    blocking or non-blocking, but will busy-loop if non-blocking and the
    contents cannot be read immediately.
</p>
</dd>
</dl></div>
<div class="paragraph"><p>During loading, the tpl image will be extensively checked for internal validity.</p></div>
<div class="paragraph"><p>This function returns 0 on success or -1 on error.</p></div>
<div class="sect3">
<h4 id="excess_ok"><tt>TPL_EXCESS_OK</tt></h4>
<div class="paragraph"><p>When reading a tpl image from a file or memory (but not from a file descriptor)
the size of the file or memory buffer must exactly equal that of the tpl image
stored therein. In other words, no excess trailing data beyond the tpl image is
permitted. The bit flag <tt>TPL_EXCESS_OK</tt> can be OR&#8217;d with <tt>TPL_MEM</tt> or <tt>TPL_FILE</tt>
to relax this requirement.</p></div>
<div class="paragraph"><p>A situation where this flag can be useful is in conjunction with <tt>tpl_dump</tt> in
the <tt>TPL_MEM|TPL_PREALLOCD</tt> mode. In this example, the program does not concern
itself with the actual tpl size as long as <tt>LEN</tt> is sufficiently large.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>char buf[LEN];  /* will store and read tpl images here */
...
tpl_dump(tn, TPL_MEM|TPL_PREALLOCD, buf, LEN);
...
tpl_load(tn, TPL_MEM|TPL_EXCESS_OK, buf, LEN);</tt></pre>
</div></div>
</div>
</div>
<div class="sect2">
<h3 id="tpl_unpack">tpl_unpack</h3>
<div class="paragraph"><p>The <tt>tpl_unpack()</tt> function unpacks data from the tpl. When data is unpacked,
it is copied to the C program variables originally specified in <tt>tpl_map()</tt>.
The first argument to <tt>tpl_unpack</tt> is the <tt>tpl_node*</tt> for the tpl and the
second argument is an <a href="#index">index number</a>.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tn = tpl_map( "A(i)A(c)", &amp;i, &amp;c );
tpl_load( tn, TPL_FILE, "nested.tpl" );
while (tpl_unpack( tn, 1) &gt; 0) printf("i is %d\n", i); /* unpack index 1 */
while (tpl_unpack( tn, 2) &gt; 0) printf("c is %c\n", c); /* unpack index 2 */</tt></pre>
</div></div>
<div class="sect3">
<h4 id="_index_number_0_2">Index number 0</h4>
<div class="paragraph"><p>It is necessary to unpack index number 0 only if the format string contains
characters that are not inside an <tt>A(...)</tt>, such as the <tt>i</tt> in the format string
<tt>iA(c)</tt>.</p></div>
</div>
<div class="sect3">
<h4 id="_variable_length_arrays_2">Variable-length arrays</h4>
<div class="sect4">
<h5 id="_unpacking_elements_from_an_array">Unpacking elements from an array</h5>
<div class="paragraph"><p>For variable-length arrays, each call to <tt>tpl_unpack()</tt> unpacks another element.
The return value can be used to tell when you&#8217;re done: if it&#8217;s positive, an
element was unpacked; if it&#8217;s 0, nothing was unpacked because there are no more
elements. A negative return value indicates an error (e.g. invalid index number).
In this document, we usually unpack variable-length arrays using a <tt>while</tt> loop:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>while( tpl_unpack( tn, 1 ) &gt; 0 ) {
    /* got another element */
}</tt></pre>
</div></div>
</div>
<div class="sect4">
<h5 id="_array_length">Array length</h5>
<div class="paragraph"><p>When unpacking a variable-length array, it may be convenient to know ahead of
time how many elements will need to be unpacked.  You can use <tt>tpl_Alen()</tt> to
get this number.</p></div>
</div>
<div class="sect4">
<h5 id="nested_unpack">Unpacking nested arrays</h5>
<div class="paragraph"><p>In a format string containing a nested variable-length array such as <tt>A(A(s))</tt>,
unpack the outer, parent array before unpacking the child array.</p></div>
<div class="paragraph"><p>When you unpack a parent array, it prepares the child array for unpacking.
After unpacking the elements of the child array, the program can repeat the
process by unpacking another parent element, then the child elements, and so on.
The example below unpacks a tpl having the format string <tt>A(A(c))</tt>.</p></div>
<div class="listingblock">
<div class="title">Unpacking nested arrays</div>
<div class="content">
<pre><tt>#include "tpl.h"
#include &lt;stdio.h&gt;

int main() {
    char c;
    tpl_node *tn;

    tn = tpl_map("A(A(c))", &amp;c);

    tpl_load(tn, TPL_FILE, "test40.tpl");
    while (tpl_unpack(tn,1) &gt; 0) {
        while (tpl_unpack(tn,2) &gt; 0) printf("%c ",c);
        printf("\n");
    }
    tpl_free(tn);
}</tt></pre>
</div></div>
<div class="paragraph"><p>The file <tt>test40.tpl</tt> is from the <a href="#nested_pack">nested packing example</a>. When
run, this program prints:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>a b
1 2 3</tt></pre>
</div></div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="tpl_free">tpl_free</h3>
<div class="paragraph"><p>The final step for any tpl is to release it using <tt>tpl_free()</tt>. Its only
argument is the <tt>tpl_node*</tt> to free.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tpl_free( tn );</tt></pre>
</div></div>
<div class="paragraph"><p>This function does not return a value (it is <tt>void</tt>).</p></div>
</div>
<div class="sect2">
<h3 id="tpl_alen">tpl_Alen</h3>
<div class="paragraph"><p>This function takes a <tt>tpl_node*</tt> and an index number and returns an <tt>int</tt>
specifying the number of elements in the variable-length array.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>num_elements = tpl_Alen(tn, index);</tt></pre>
</div></div>
<div class="paragraph"><p>This is mainly useful for programs that unpack data and need to know ahead of
time the number of elements that will need to be unpacked. (It returns the
current number of elements; it will decrease as elements are unpacked).</p></div>
</div>
<div class="sect2">
<h3 id="tpl_peek">tpl_peek</h3>
<div class="paragraph"><p>This function peeks into a file or a memory buffer containing a tpl image
and returns a copy of its format string.  It can also peek at the lengths of
any fixed-length arrays in the format string, or it can also peek into the data
stored in the tpl.</p></div>
<div class="sect3">
<h4 id="_format_peek">Format peek</h4>
<div class="paragraph"><p>The format string can be obtained
like this:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>fmt = tpl_peek(TPL_FILE, "file.tpl");
fmt = tpl_peek(TPL_MEM, addr, sz);</tt></pre>
</div></div>
<div class="paragraph"><p>On success, a copy of the format string is returned. The caller must eventually
free it. On error, such as a non-existent file, or an invalid tpl image, it
returns <tt>NULL</tt>.</p></div>
</div>
<div class="sect3">
<h4 id="_array_length_peek">Array length peek</h4>
<div class="paragraph"><p>The lengths of all fixed-length arrays in the format string can be queried using
the <tt>TPL_FXLENS</tt> mode. It provides the number of such fixed-length arrays and
their lengths. If the former is non-zero, the caller must free the latter array
when finished. The format string itself must also be freed.</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>uint32_t num_fxlens, *fxlens, j;
fmt = tpl_peek(TPL_FILE|TPL_FXLENS, filename, &amp;num_fxlens, &amp;fxlens);
if (fmt) {
  printf("format %s, num_fxlens %u\n", fmt, num_fxlens);
  for(j=0; j&lt;num_fxlens; j++) printf("fxlens[%u] %u\n", j, fxlens[j]);
  if (num_fxlens &gt; 0) free(fxlens);
  free(fmt);
}</tt></pre>
</div></div>
<div class="paragraph"><p>The <tt>TPL_FXLENS</tt> mode is mutually exclusive with <tt>TPL_DATAPEEK</tt>.</p></div>
</div>
<div class="sect3">
<h4 id="_data_peek">Data peek</h4>
<div class="paragraph"><p>To peek into the data, additional arguments are used. This is a quick
alternative to mapping, loading and unpacking the tpl, but peeking is limited
to the data in index 0. In other words, no peeking into <tt>A(...)</tt> types.
Suppose the tpl image in <tt>file.tpl</tt> has the format string <tt>siA(i)</tt>. Then the
index 0 format characters are <tt>si</tt>. This is how to peek at their content:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>char *s;
int i;
fmt = tpl_peek(TPL_FILE | TPL_DATAPEEK, "file.tpl", "si", &amp;s, &amp;i);</tt></pre>
</div></div>
<div class="paragraph"><p>Now <tt>s</tt>, <tt>i</tt>, and <tt>fmt</tt> have been populated with data.  The caller must
eventually free <tt>fmt</tt> and <tt>s</tt> because they are allocated strings.
Of course, it works with <tt>TPL_MEM</tt> as well as <tt>TPL_FILE</tt>.  Notice that
<tt>TPL_DATAPEEK</tt> was OR&#8217;d with the mode. You can also specify <em>any leading
portion</em> of the index 0 format if you don&#8217;t want to peek at the whole thing:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>fmt = tpl_peek(TPL_FILE | TPL_DATAPEEK, "file.tpl", "s", &amp;s);</tt></pre>
</div></div>
<div class="paragraph"><p>The <tt>TPL_DATAPEEK</tt> mode is mutually exclusive with <tt>TPL_FXLENS</tt>.</p></div>
<div class="sect4">
<h5 id="_structure_peek">Structure peek</h5>
<div class="paragraph"><p>Lastly you can peek into <tt>S(...)</tt> structures in index 0, but omit the
surrounding <tt>S(...)</tt> in the format, and specify an argument to receive
each structure member individually. You can specify any leading portion
of the structure format. For example if <tt>struct.tpl</tt> has the format string
<tt>S(si)</tt>, you can peek at its data in these ways:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>fmt = tpl_peek(TPL_FILE | TPL_DATAPEEK, "struct.tpl", "s", &amp;s);
fmt = tpl_peek(TPL_FILE | TPL_DATAPEEK, "struct.tpl", "si", &amp;s, &amp;i);</tt></pre>
</div></div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="tpl_jot">tpl_jot</h3>
<div class="paragraph"><p>This is a quick shortcut for generating a tpl. It can be used instead of the
usual "map, pack, dump, and free" lifecycle. With <tt>tpl_jot</tt> all those steps are
handled for you.  It only works for simple formats-- namely, those without
<tt>A(...)</tt> in their format string. Here is how it is used:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>char *hello = "hello", *world = "world";
tpl_jot( TPL_FILE, "file.tpl", "ss", &amp;hello, &amp;world);</tt></pre>
</div></div>
<div class="paragraph"><p>It supports the three standard modes, <tt>TPL_FILE</tt>, <tt>TPL_FD</tt> and <tt>TPL_MEM</tt>.
It returns -1 on failure (such as a bad format string or error writing the
file) or 0 on success.</p></div>
</div>
<div class="sect2">
<h3 id="hooks">tpl_hook</h3>
<div class="paragraph"><p>Most users will just leave these hooks at their default values. You can change
these hook values if you want to modify tpl&#8217;s internal memory management and
error reporting behavior.</p></div>
<div class="paragraph"><p>A global structure called <tt>tpl_hook</tt> encapsulates the hooks.  A program can
reconfigure any hook by specifying an alternative function whose prototype
matches the default. For example:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>#include "tpl.h"
extern tpl_hook_t tpl_hook;</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>int main() {
    tpl_hook.oops = printf;
    ...
}</tt></pre>
</div></div>
<div class="tableblock">
<table rules="none"
width="90%"
frame="border"
cellspacing="0" cellpadding="4">
<caption class="title">Table 3. Configurable hooks</caption>
<col width="33%" />
<col width="33%" />
<col width="33%" />
<thead>
<tr>
<th align="left" valign="top">Hook                </th>
<th align="left" valign="top">Description                  </th>
<th align="left" valign="top"> Default</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="top"><p class="table"><tt>tpl_hook.oops</tt></p></td>
<td align="left" valign="top"><p class="table">log error messages</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_oops</tt></p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table"><tt>tpl_hook.malloc</tt></p></td>
<td align="left" valign="top"><p class="table">allocate memory</p></td>
<td align="left" valign="top"><p class="table"><tt>malloc</tt></p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table"><tt>tpl_hook.realloc</tt></p></td>
<td align="left" valign="top"><p class="table">reallocate memory</p></td>
<td align="left" valign="top"><p class="table"><tt>realloc</tt></p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table"><tt>tpl_hook.free</tt></p></td>
<td align="left" valign="top"><p class="table">free memory</p></td>
<td align="left" valign="top"><p class="table"><tt>free</tt></p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table"><tt>tpl_hook.fatal</tt></p></td>
<td align="left" valign="top"><p class="table">log fatal message and exit</p></td>
<td align="left" valign="top"><p class="table"><tt>tpl_fatal</tt></p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table"><tt>tpl_hook.gather_max</tt></p></td>
<td align="left" valign="top"><p class="table">tpl_gather max image size</p></td>
<td align="left" valign="top"><p class="table"><tt>0 (unlimited)</tt></p></td>
</tr>
</tbody>
</table>
</div>
<div class="sect3">
<h4 id="_the_oops_hook">The oops hook</h4>
<div class="paragraph"><p>The <tt>oops</tt> has the same prototype as <tt>printf</tt>. The built-in default oops
handling function writes the error message to <tt>stderr</tt>.</p></div>
</div>
<div class="sect3">
<h4 id="_the_fatal_hook">The fatal hook</h4>
<div class="paragraph"><p>The fatal hook is invoked when a tpl function cannot continue because of an out-
of-memory condition or some other usage violation or inconsistency. It has this
prototype:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>void fatal_fcn(char *fmt, ...);</tt></pre>
</div></div>
<div class="paragraph"><p>The <tt>fatal</tt> hook must not return. It must either exit, <em>or</em> if the program needs
to handle the failure and keep executing, <tt>setjmp</tt> and <tt>longjmp</tt> can be used.
The default behavior is to <tt>exit(-1)</tt>.</p></div>
<div class="listingblock">
<div class="title">Using longjmp in a fatal error handler</div>
<div class="content">
<pre><tt>#include &lt;setjmp.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdarg.h&gt;
#include "tpl.h"

jmp_buf env;
extern tpl_hook_t tpl_hook;

void catch_fatal(char *fmt, ...) {
  va_list ap;

  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
  longjmp(env,-1);                /* return to setjmp point */
}

int main() {
  int err;
  tpl_node *tn;
  tpl_hook.fatal = catch_fatal;    /* install fatal handler */

  err = setjmp(env); /* on error, control will return here  */
  if (err) {
    printf("caught error!\n");
    return -1;
  }

  tn = tpl_map("@");              /* generate a fatal error */
  printf("program ending, without error\n");
  return 0;
}</tt></pre>
</div></div>
<div class="paragraph"><p>This example is included in <tt>tests/test123.c</tt>. When run, this program prints:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>unsupported option @
failed to parse @
caught error!</tt></pre>
</div></div>
</div>
</div>
<div class="sect2">
<h3 id="_tpl_gather">tpl_gather</h3>
<div class="sidebarblock">
<div class="content">
<div class="title">Most programs don&#8217;t need this</div>
<div class="paragraph"><p>Normally, <tt>tpl_load()</tt> is used to read a tpl image having an expected format
string.  A more generic operation is to acquire a tpl image whose format string is
unknown. E.g., a generic message-receiving function might gather tpl images of
varying format and route them to their final destination. This is the purpose of
<tt>tpl_gather</tt>. It produces a memory buffer containing one tpl image. If there
are multiple contiguous images in the input, it gathers exactly one image at a
time.</p></div>
</div></div>
<div class="paragraph"><p>The prototype for this function is:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>int tpl_gather( int mode, ...);</tt></pre>
</div></div>
<div class="paragraph"><p>The <tt>mode</tt> argument is one of three constants listed below, which must be
followed by the mode-specific required arguments:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>TPL_GATHER_BLOCKING,    int fd, void **img, size_t *sz
TPL_GATHER_NONBLOCKING, int fd, tpl_gather_t **gs, tpl_gather_cb *cb, void *data
TPL_GATHER_MEM,         void *addr, size_t sz, tpl_gather_t **gs, tpl_gather_cb *cb, void *data</tt></pre>
</div></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="title"><tt>tpl_hook.gather_max</tt></div>All modes honor <tt>tpl_hook.gather_max</tt>, specifying the maximum byte size for a
tpl image to be gathered (the default is unlimited, signified by 0). If a source
attempts to send a tpl image larger than this maximum, whatever partial image
has been read will be discarded, and no further reading will take place; in this
case <tt>tpl_gather</tt> will return a negative (error) value to inform the caller that
it should stop gathering from this source, and close the originating file
descriptor if there is one. (The whole idea is to prevent untrusted sources from
sending extremely large tpl images which would consume too much memory.)</td>
</tr></table>
</div>
<div class="sect3">
<h4 id="_tt_tpl_gather_blocking_tt"><tt>TPL_GATHER_BLOCKING</tt></h4>
<div class="paragraph"><p>In this mode, <tt>tpl_gather</tt> blocks while reading file descriptor <tt>fd</tt> until one
complete tpl image is read. No bytes past the end of the tpl image will be read.
The address of the buffer containing the image is returned in <tt>img</tt> and its size
is placed in <tt>sz</tt>. The caller is responsible for eventually freeing the buffer.
The function returns 1 on success, 0 on end-of-file, or a negative number on
error.</p></div>
</div>
<div class="sect3">
<h4 id="_tt_tpl_gather_nonblocking_tt"><tt>TPL_GATHER_NONBLOCKING</tt></h4>
<div class="paragraph"><p>This mode is for non-blocking, event-driven programs that implement their
own file descriptor readability testing using <tt>select()</tt> or the like. In this
mode, tpl images are gathered in chunks as data becomes readable. Whenever a
full tpl image has been gathered, it invokes a caller-specified callback to do
something with the image.  The arguments are the file descriptor <tt>fd</tt> which the
caller has determined to be readable and which must be in non-blocking mode, a
pointer to a file-descriptor-specific handle which the caller has declared
(explained below); a callback to invoke when a tpl image has been read; and an
opaque pointer that will passed to the callback.</p></div>
<div class="paragraph"><p>For each file descriptor on which <tt>tpl_gather</tt> will be used, the caller must
declare a <tt>tpl_gather_t*</tt> and initialize it to <tt>NULL</tt>. Thereafter it will be
used internally by <tt>tpl_gather</tt> whenever data is readable on the descriptor.</p></div>
<div class="paragraph"><p>The callback will only be invoked whenever <tt>tpl_gather()</tt> has accumulated one
complete tpl image. It must have this prototype:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>int (tpl_gather_cb)(void *img, size_t sz, void *data);</tt></pre>
</div></div>
<div class="paragraph"><p>The callback can do anything with the tpl image but it must not free it. It can
be copied if it needs to survive past the callback&#8217;s return. The callback should
return 0 under normal circumstances, or a negative number to abort; that is,
returning a negative number causes <tt>tpl_gather</tt> itself to discard any remaining
full or partial tpl images that have been read, and to return a negative number
(-4 in particular) to signal its caller to close the file descriptor.</p></div>
<div class="paragraph"><p>The return value of <tt>tpl_gather()</tt> is negative if an error occurred or 0 if a
normal EOF was encountered-- both cases require that the caller close the file
descriptor (and stop monitoring it for readability, obviously). If the return
value is positive, the function succeeded in gathering whatever data was
currently readable, which may have been a partial tpl image, or one or more
complete images.</p></div>
<div class="sect4">
<h5 id="_typical_usage">Typical Usage</h5>
<div class="paragraph"><p>The program will have established a file descriptor in non-blocking mode and
be monitoring it for readability, using <tt>select()</tt>. Whenever it&#8217;s readable, the
program calls <tt>tpl_gather()</tt>. In skeletal terms:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>tpl_gather_t *gt=NULL;
int rc;</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>void fd_is_readable(int fd) {
  rc = tpl_gather( TPL_GATHER_NONBLOCKING, fd, &amp;gt, callback, NULL );
  if (rc &lt;= 0) {
      close(fd);               /* got eof or fatal */
      stop_watching_fd(fd);
  }
}</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>int callback( void *img, size_t sz, void *data ) {
  printf("got a tpl image\n"); /* do something with img. do not free it. */
  return 0;                    /* normal (no error) */
}</tt></pre>
</div></div>
</div>
</div>
<div class="sect3">
<h4 id="_tt_tpl_gather_mem_tt"><tt>TPL_GATHER_MEM</tt></h4>
<div class="paragraph"><p>This mode is identical to <tt>TPL_GATHER_NONBLOCKING</tt> except that it gathers from a
memory buffer instead of from a file descriptor. In other words, if some other
layer of code-- say, a decryption function (that is decrypting fixed-size
blocks) produces tpl fragments one-by-one, this mode can be used to reconstitute
the tpl images and invoke the callback for each one. Its parameters are the same
as for the <tt>TPL_GATHER_NONBLOCKING</tt> mode except that instead of a file
descriptor, it takes a buffer address and size. The return values are also the
same as for <tt>TPL_GATHER_NONBLOCKING</tt> noting of course there is no file
descriptor to close on a non-positive return value.</p></div>
</div>
</div>
</div>
</div>
</div>
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